There's a difference between reading and writing, and reading and writing well. I would expect the tests to expect higher proficiency than what is expected in your usual text messages.
Texting is unironically a better use of time than reading infinite jest, or gravities rainbow, etc.
... “How do you feel, Jake?” “Fine, it doesn’t hurt much.” “Are you all right?” ...
(Hemmingway)
First: Your HS kids hang out with a different crowd than my HS kids :-)
Second: This is about reading ability (comprehension, etc), not literature. Whether the quality of a text message is superior/inferior to whatever they use in literature classes is irrelevant.